The definition of revenge here is complicated. To my mind, there are two forms of revenge:
1) When revenge is in balance with the initial damage caused. This could be seen as righting a wrong, a form of justice. For example, someone steals money from you, so you steal the equivalent amount back from them.
2) When revenge exceeds the initial hurt. In this case, someone has stolen money from you, so you kidnap their entire family. This is, obviously, out of balance.
I would certainly say that the balanced and just form of revenge is necessary to right the wrong, especially when the person who is the recipient of this revenge will learn from their initial error. Revenge that exceeds justice, however, will not provide a moralising outcome. Rather, it will teach that, if a wrong is done to you, it is okay to enact further and exaggerated pain for your own satisfaction, instead of a teach a lesson.